This invention relates to a liquid heating apparatus in which a heat exchanger, such as boiler, making use of combustion gas up/down-draft method is installed within a water tank.
The liquid heating apparatus described above includes those proposed by this applicant and disclosed in (A) the Japanese Utility Model Publication No. 44093/1973 and (B) the Japanese Utility Model Publication No. 15168/1976. What is disclosed in (A) is the one as shown in FIGS. 9 to 12, with a heat exchanger 21 provided in a water tank 22; said heat exchanger 21 comprising a partitioned water chamber 25 provided within an internal void section surrounded by a heat receiving wall 23 with the upper section and both sides of the lower section communicated with a communicating tube 24 and a water through hole 30 respectively to a water tank 22, a combustion chamber 26 communicated to a gas up-draft chamber 29 having a narrow upper section formed in one side thereof and a gas down-draft chamber 27 having a narrow lower section formed in the other side with upper sections of the two chambers 27 and 29 communicated to each other with gas through holes 28 formed in both sides of the communicating tube 24, a combustor 33 provided in the lower section of the combustion chamber 26 with an air supply path 31 to the combustion chamber 26 and an exhaust path 32 to the gas down-draft chamber 27 each provided in the lower section thereof.
Description is made hereinafter for phenomena in up/down-draft of combustion gas in the heat exchanger 21 as described above. In a gas combustion path having the gas up-draft chamber 29 shown in FIG. 11 and the gas down-draft chamber 27 having the same height H as that of the gas up-draft chamber, it is known that an internal draft power Pch as expressed by the following equations (1) and (2) is generated, assuming a heat generating point U, a middle point M, and an exhaust point EQU D: Pch=(.gamma.d-.gamma.u).times.H (1) EQU Pch=(PH/R)(1/Td-1/Tu) (2)
Herein;
.gamma.d: Specific weight of combustion gas in the gas down-flow chamber 27
.gamma.u: Specific weight of combustion gas in the gas up-flow chamber 29
H: Height of the middle point M from the heat generating point U
P: Pressure of the combustion gas
R: Constant for the combustion gas
Td: Temperature of the combustion gas in the gas down-flow chamber 27
Tu: Temperature of combustion gas in the gas up-flow chamber 29
As Tu is always higher than Td (Tu&gt;Td), when the heat exchanger 21 is working, namely when the combustor 33 is working, (1/Td-1/Tu)&gt;0, and the combustion gas flows from the heat generating point U to the middle point M and to the exhaust point D. In contrast to it, when operation of the heat exchanger 21 is down, Tu=Td=Temperature of peripheral water, and for this reason the internal draft power Pch=0, so that a combustion gas in a combustion gas path stops flowing and resides therein, which is useful in preventing cool air from coming in from the outside and keeping the internal temperature at a level.
What was described above is based on this principle, and a combustion gas generated within the combustion chamber 26 goes up in the gas up-draft chamber 29 and then goes down in the gas down-draft chamber 27 radiating heat with the temperature of the gas becoming lower and the weight becoming heavier and is exhausted through a flue 32 from the exhaust path 34 to the outside, and in this process the combustion gas contacts the heat receiving wall 23 and walls of the partitioned water chamber 25 to heat water within the water tank 22 so that the heat exchange is high, temperature of the water goes up rapidly, temperature drop of a combustion gas while flowing is large with the down-draft fluidity raised and the draft function promoted. In addition as the two paths 31 and 32 adjoin each other, a supply air flowing in the air supply path 31 is heated by exhaust gas flowing in the gas exhaust path 32 with the combustion efficiency raised, which is another merit of the system above.
In the apparatus disclosed in (A) above, however, the partitioned water chamber 25 is flat, so that the heat transfer area is small and the heat transfer efficiency is low, and in addition, as there is a clearance between a bottom face of the water tank 22 and that of the heat exchanger 21, convection fault occurs in the water residing in this section, which prevents all portions of the water from being heated evenly. Heat exchange is carried out more smoothly in the heat receiving wall 23 in the side of gas up-draft chamber 29 which is located in the opposite side to the heat receiving wall 23 and where water convection is carried out more smoothly than in the heat receiving wall 23 in the side of gas down-draft chamber 27 which is located near a wall face of the water tank 22 and where water convection is not carried out smoothly, and as a result combustion gas residing in the gas up-draft chamber 29 is cooled, and a satisfactory draft power can hardly be obtained.
Furthermore in the apparatus described above, the exhaust point D (FIG. 12) is located at a position higher by the range h from the exhaust point D, pressures Pu, Pm and Pd at points U, M and D respectively are calculated from the aforesaid equations (1) and (2) as follows. ##EQU1## And Pd is released to the atmosphere, Pd=Po (Atmospheric pressure). For this reason, the following equations are provided: EQU Po=Pm+.gamma.d.H-.gamma.d.h (5) EQU Pm=Po-.gamma.d.H+.gamma.d.h (6)
and applying these into the equation (3), the following equation can be obtained. ##EQU2##
Herein, while operations of the heat exchanger 21 are down, .gamma.d is equal to .gamma.u (.gamma.d=.gamma.u), so Pu=Po+.gamma.d.h, namely Pu-Po=.gamma.d.h&gt;0, so that the relation of Pu&gt;Po is always maintained, and the combustion gas in the combustion gas path always flow from the heating point U to the middle point M to the exhaust point D without residing in the combustion gas path, and for this reason intrusion of the external air into the inside is not prevented and heat of hot water inside the water tank 22 is radiated to the outside.
The apparatus disclosed in (B) above is like the one shown in FIG. 13 and FIG. 14, wherein an internal drum 67 comprising a dual wall is provided in and at a space from an external drum 66 also comprising a dual wall, a combustion gas down-draft chamber 68 is provided between them, an external water chamber 71 having a hot water outlet port 69 and a water supply port 70 in the upper and lower sections thereof is provided outside of the the combustion gas down-draft chamber 68, a combustion chamber 74 communicating in the upper section thereof to the combustion gas down-draft chamber 68 is provided in the internal drum 67, and exhaust port 75 is provided in the lower section of the combustion gas chamber 68, an exhaust cylinder 78 is connected to this exhaust cylinder 78, and a combustor 77 is provided disconnectably through the inner and outer water chambers 71, 72. The hot water outlet port 69 is connected to hot water reserving sections such as water tanks not shown herein with appropriate pipings, and the numeral 79 indicates a port for cleaning. In the liquid heating apparatus as described above, a combustion gas gradually caused to satisfy the rating by the combustor 77 by means of up/down draft method rises in the combustion chamber 74 with the heat radiated from the combustion gas being absorbed, then reverses in the upper section thereof and flows down at a velocity g (m/sec) in the combustion gas down-draft chamber 68, being accelerated to a velocity G (m/sec) at the exhaust port 75 and exhausted therefrom. On the other hand, water is supplied from the water supply port 70 in the lower section thereof to the outer external water chamber 71, rises in this external water chamber 71 and the internal water chamber 72 communicated thereto with the communicating tubes 73 in the upper and lower sections thereof, while the combustion gas causes the temperature of the liquid to rapidly rise by raising the heat exchange rate between the combustion gas and the liquid because the combustion gas supplies a liquid in the internal and external water chambers 71, 72 with enough quantity of heat by means of radiation and thermal conduction and the down-draft fluidity of the combustion gas in the combustion gas down-draft chamber 68 is raised, which advantageously improves the combustion efficiency and prevents incomplete combustion.
The aforesaid apparatus has the advantages as described above, but at the same time it has problems as described below. Namely in this liquid heating apparatus, as water is supplied from the water supply port 70 located in the lower section thereof to the external water chamber 71 and rises in this external water chamber 71 as well as in the internal water chamber 72 communicated with the communicating tubes 73 in the upper and lower sections thereof to the external water chamber 71, interference is generated between cool water rising in the external water chamber 71 and hot water exhausted in the upper section thereof from the internal water chamber 72 and again descending the external water chamber 71, which prevents water from smoothly convecting in both the internal and external water chambers, and for this reason an efficient heat exchange between the gas and the water can not be achieved, and also as the entire apparatus is monolithically assembled to form a heat exchanging/water reserving section, the work for installation is difficult, and in addition cleaning inside the external water chamber 71 is extremely difficult.